Obama: 'Al Qaeda is under more pressure than at any time since 9/11'

President Obama: "We have taken out more than half of al Qaeda's leadership"

"Al Qaeda is under more pressure than at any time since 9/11," Obama says

Obama says 33,000 "surge" troops will be out of Afghanistan in 15 months

(CNN) -- Information collected by U.S. commandos following a raid that resulted in the killing of al Qaeda leader Osama bin Laden shows the terror group is under enormous strain, President Barack Obama said in a nationally televised address.

It was the most public account to date by the president about what the information taken from bin Laden's Abbottabad, Pakistan, compound revealed about the state of al Qaeda.

"Bin Laden expressed concern that al Qaeda has been unable to effectively replace senior terrorists that have been killed, and that al Qaeda has failed in its effort to portray America as a nation at war with Islam -- thereby draining more widespread support," Obama said Wednesday as part of an announcement of a timetable to withdraw U.S. troops from Afghanistan.

Obama said the 33,000 additional forces he ordered to Afghanistan in December 2009 will be withdrawn within 15 months, with the remaining 70,000 troops withdrawn by 2014.

"We are starting this drawdown from a position of strength. Al Qaeda is under more pressure than at any time since 9/11," Obama said.

"Together with the Pakistanis, we have taken out more than half of al Qaeda's leadership. And thanks to our intelligence professionals and Special Forces, we killed Osama bin Laden, the only leader that al Qaeda has ever known."

But Obama acknowledged that al Qaeda remains dangerous, and the United States must be vigilant against attacks.

There hasn't been a successful major attack on the West by al Qaeda since the London bombings in 2005, and experts are divided over whether al Qaeda's new leader, Ayman al-Zawahiri, will try to cement his throne with a dastardly act.

Al-Zawahiri takes charge after a series of recent captures and kills of al Qaeda leaders: Among them were Fazul Abdullah Mohammed, the most-wanted terrorist in Africa, and Ilyas Kashmiri in Pakistan.

"Between the drone program, losing the war of ideas, their relevance, the bench depleted by captures or kills, the lack of success of attacks on the West -- all these things don't suggest a great deal of strength for al Qaeda," said Peter Bergen, CNN's national security analyst.

The biggest challenge for al Qaeda may be how to gain back ideological ground in a time when pro-democracy movements are blossoming in northern Africa and the Middle East.

Al Qaeda has been opportunistic in claiming that the mass demonstrations fly in the face of Western powers, but in reality, Bergen said, the group has been rendered irrelevant in the events reverberating through the region.

"If you have freedom, al Qaeda will go away," former Egyptian jihadist Osama Rushdi said in February.

Had bin Laden been killed shortly after the 9/11 attacks, al-Zawahiri would have been taking over a less mature organization and might have had a more difficult time moving it forward, said Bill Roggio, a military affairs analyst who is managing editor of The Long War Journal.

But 10 years after those devastating attacks, al Qaeda is well-established, Roggio said.